Merge pull request #39 from clue-labs/residual-parallel

Fix option to merge parallel edges when creating residual graph

Author: clue

src/ResidualGraph.php

@@ -2,12 +2,10 @@
 
 namespace Graphp\Algorithms;
 
-use Graphp\Algorithms\BaseGraph;
-use Fhaculty\Graph\Exception\UnexpectedValueException;
-
-use Fhaculty\Graph\Graph;
 use Fhaculty\Graph\Edge\Base as Edge;
 use Fhaculty\Graph\Edge\Directed as EdgeDirected;
+use Fhaculty\Graph\Exception\UnexpectedValueException;
+use Fhaculty\Graph\Graph;
 
 class ResidualGraph extends BaseGraph
 {
@@ -90,20 +88,22 @@ public function createGraph()
      */
     private function mergeParallelEdges(Edge $newEdge)
     {
-        $parallelEdges = $newEdge->getEdgesParallel();
-        if ($parallelEdges) {
+        $alg = new Parallel($this->graph);
+        $parallelEdges = $alg->getEdgesParallelEdge($newEdge)->getVector();
 
-            $mergedCapacity = 0;
+        if (!$parallelEdges) {
+            return;
+        }
 
-            foreach ($parallelEdges as $parallelEdge) {
-                $mergedCapacity += $parallelEdge->getCapacity();
-            }
+        $mergedCapacity = 0;
+        foreach ($parallelEdges as $parallelEdge) {
+            $mergedCapacity += $parallelEdge->getCapacity();
+        }
 
-            $newEdge->setCapacity($newEdge->getCapacity() + $mergedCapacity);
+        $newEdge->setCapacity($newEdge->getCapacity() + $mergedCapacity);
 
-            foreach ($parallelEdges as $parallelEdge) {
-                $parallelEdge->destroy();
-            }
+        foreach ($parallelEdges as $parallelEdge) {
+            $parallelEdge->destroy();
         }
     }
 }

tests/ResidualGraphTest.php

@@ -1,9 +1,7 @@
 <?php
 
-use Fhaculty\Graph\Exception\UnexpectedValueException;
-use Fhaculty\Graph\Edge\Base as Edge;
-use Graphp\Algorithms\ResidualGraph;
 use Fhaculty\Graph\Graph;
+use Graphp\Algorithms\ResidualGraph;
 
 class ResidualGraphTest extends TestCase
 {
@@ -87,6 +85,81 @@ public function testEdgePartial()
         $this->assertGraphEquals($expected, $residual);
     }
 
+    public function testResidualGraphCanOptionallyKeepNullCapacityForEdgeWithZeroFlow()
+    {
+        // 1 -[0/2]-> 2
+        $graph = new Graph();
+        $v1 = $graph->createVertex(1);
+        $v2 = $graph->createVertex(2);
+        $v1->createEdgeTo($v2)->setFlow(0)->setCapacity(2);
+
+        // 1 -[0/2]-> 2
+        // ^          |
+        // \--[0/0]---/
+        $expected = new Graph();
+        $v1 = $expected->createVertex(1);
+        $v2 = $expected->createVertex(2);
+        $v1->createEdgeTo($v2)->setFlow(0)->setCapacity(2);
+        $v2->createEdgeTo($v1)->setFlow(0)->setCapacity(0);
+
+        $alg = new ResidualGraph($graph);
+        $alg->setKeepNullCapacity(true);
+        $residual = $alg->createGraph();
+
+        $this->assertGraphEquals($expected, $residual);
+    }
+
+    public function testResidualGraphCanOptionallyKeepNullCapacityForEdgeWithZeroCapacityRemaining()
+    {
+        // 1 -[2/2]-> 2
+        $graph = new Graph();
+        $v1 = $graph->createVertex(1);
+        $v2 = $graph->createVertex(2);
+        $v1->createEdgeTo($v2)->setFlow(2)->setCapacity(2);
+
+        // 1 -[0/0]-> 2
+        // ^          |
+        // \--[0/2]---/
+        $expected = new Graph();
+        $v1 = $expected->createVertex(1);
+        $v2 = $expected->createVertex(2);
+        $v1->createEdgeTo($v2)->setFlow(0)->setCapacity(0);
+        $v2->createEdgeTo($v1)->setFlow(0)->setCapacity(2);
+
+        $alg = new ResidualGraph($graph);
+        $alg->setKeepNullCapacity(true);
+        $residual = $alg->createGraph();
+
+        $this->assertGraphEquals($expected, $residual);
+    }
+
+    public function testParallelEdgesCanBeMerged()
+    {
+        // 1 -[1/2]-> 2
+        // |          ^
+        // \--[2/3]---/
+        $graph = new Graph();
+        $v1 = $graph->createVertex(1);
+        $v2 = $graph->createVertex(2);
+        $v1->createEdgeTo($v2)->setFlow(1)->setCapacity(2);
+        $v1->createEdgeTo($v2)->setFlow(2)->setCapacity(3);
+
+        // 1 -[0/2]-> 2
+        // ^          |
+        // \--[0/3]---/
+        $expected = new Graph();
+        $v1 = $expected->createVertex(1);
+        $v2 = $expected->createVertex(2);
+        $v1->createEdgeTo($v2)->setFlow(0)->setCapacity(2);
+        $v2->createEdgeTo($v1)->setFlow(0)->setCapacity(3);
+
+        $alg = new ResidualGraph($graph);
+        $alg->setMergeParallelEdges(true);
+        $residual = $alg->createGraph();
+
+        $this->assertGraphEquals($expected, $residual);
+    }
+
     /**
      * expect exception for undirected edges
      * @expectedException UnexpectedValueException